One way of significantly enhancing the performance of air/liquid heat exchangers is to install one or more spray bars to spray a liquid onto their heat transfer surface to thereby utilize the latent heat of evaporation of this liquid to boost the heat transfer. The sprayed liquid is vaporized as it passes through the air side flow circuit of the heat exchanger, and the heat removed through evaporation is added to the sensible heat normally removed by the cooling air. This performance enhancement can be used to increase the overall heat transfer capacity of the heat exchanger and/or reduce the cooling air mass flow required while maintaining constant heat transfer performance.
For example, in high performance piston engine powered/propeller driven aircraft where sufficient heat transfer performance is available to cool the engine(s) without evaporative cooling, a very significant reduction in the air drag on the aircraft can be achieved with the addition of evaporative cooling by the resulting reduction in the cooling air then required for the heat exchanger(s). This can be a very significant advantage recognizing that the heat exchanger(s) on a high performance aircraft can represent as much as about 50% of the total drag. Moreover, some high performance automotive as well as aircraft engines require higher cooling system operating pressures (e.g. 50 psi) to prevent water pump cavitation due to increased coolant flow requirements and the design of the water pump passages. And most special high performance radiators that meet these high pressure requirements have lower heat transfer capacity than conventional high efficiency passenger cars at these pressures. In order to operate the latter radiators at these high pressures, it has been the practice to install tie rods that limit core and header plate deflection to provide acceptable durability. But then these reinforcement rods when arranged across the core face also adversely add air flow restriction.